Focus on the pursuit and uncertainty of achieving the reward increases motivation. Focus on the reward itself and uncertainty decreases motivation.
Another way of putting this: focus on the process and uncertainty spurs you on; focus on the outcome and uncertainty makes you stumble.
Basically, moderate challenge motivates effort. Make a task too easy and it becomes boring. Make a task too hard and it becomes daunting. There is a sweet spot of challenge, which is another way of saying there is an optimal degree of uncertainty: you’re kinda optimistic you can do it and that keeps you going. But you’re not absolutely sure.
Making progress keeps you optimistic and leads to continued engagement with the task, even in the face of occasional failures.
Uncertainty energizes effort in the right conditions. It makes effort fun.
We’re more likely to achieve long-term goals when we focus on the process and not the outcome. Focusing on the outcome may get us going but for many of us it won’t keep us going. For that you need progress and just the right amount of uncertainty.
Education psychology, cognitive science, consumer research, and my own personal experience says it is so.
Inspiration:
Luxi Shen, Ayelet Fishbach, Christopher K. Hsee; The Motivating-Uncertainty Effect: Uncertainty Increases Resource Investment in the Process of Reward Pursuit, Journal of Consumer Research, Volume 41, Issue 5, 1 February 2015, Pages 1301–1315, https://doi.org/10.1086/679418